Seiko RC-4000

A wristwatch with anEIA-232 interface. A clip fitted round the watch and made electrical contact. This clip had a socketfor a stereo style jack lead the other end of which was a 25-way D-type connector. The lead allowed you to enter phone numbersetc. into the watch without having to play with tinybuttons. It also meant if the battery on your watch ran out you could restore the data without having to type it all in again.